Even as advertisers are embracing new configurations of families — two dads, say, or grandparents raising grandchildren — there’s one group that feels left out.

Women who are childless. Or as they also call themselves, the child-free. Or even the NotMoms.

According to census figures, more women in the United States are childless than at any other time since the government began keeping track in 1976. Nearly half of women — 47.6 percent — between the ages of 15 and 44 did not have children in 2014, up from 46.5 percent in 2012. And 15.3 percent of women ages 40 to 44 are childless. The numbers are growing internationally as well.

Despite these statistics, “the majority of marketing talks to adult women like they are all moms or want to be mothers,” said Adrianna Bevilaqua, chief creative officer at M Booth, a public relations company.

Melanie Notkin has made a career of catering to women who don’t have children but love them — she is the founder of the website SavvyAuntie; coined the term “professional aunt, no kids,” or PANKs; and is the author of “Otherhood: Modern Women Finding a New Kind of Happiness.” She wonders why companies, always eager to target a potentially lucrative demographic, seem to be ignoring this one.

The childless woman is “left off the table,” Ms. Notkin said. “Advertisers don’t know how to pitch to her.”

Maria Bailey, chief executive of the marketing firm BSM Media and an author of books about marketing to mothers, estimates that about 60 percent of all women shown in commercials are moms; with certain products, like toys, the percentage is much higher.

One issue is simple inertia — for years advertisers have followed research that says the mother is the main household purchaser. Ms. Bailey said mothers spent $3.4 trillion in 2015, “the largest spending consumer group in the U.S.”

Another issue is how to portray the concept of being childless. If two women are sitting on the couch chatting about, say, yogurt or a smartphone, who knows, or even cares, if they have children?

“It’s an extremely complex subject,” said Bridget Brennan, chief executive of the Female Factor, a consulting firm, and author of “Why She Buys.” “Women may be childless by choice or by chance. It’s very difficult to define assumptions about this market.”

It’s true that people tend to view those who choose not to have children differently from those who can’t have children. Those who are single and childless are perceived differently from couples without children.

But Karen Malone Wright, who founded the website TheNotMom.com, said it was less about differentiating between all these factors and more about being inclusive. Ms. Wright, who is 60 and married and does not have children, ran the first NotMom summit meeting last year in Cleveland, where she lives.

“For example, it seems that vacation advertising focuses on the extremes of female travelers — you’re hot and single or a mom with more than one child,” she said. “You’re not older, you’re not with a girlfriend.

“And although it’s beginning to change, it’s still difficult to find a paper towel commercial that doesn’t involve a kid knocking over a glass of milk,” she said. But the fact is, a lot of women and couples without children have pets and “everyone knows paper towels are very good for picking up pet vomit,” she said.

An ad featuring a woman without a child may not mean much — or even be noticed — by the broader population, Ms. Wright said, but it would mean the world to her and like-minded women, “and we’d be more likely to buy the brand.”

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A Lands’ End catalog cover from 2014 aimed at childless women.

When Lands’ End put a beaming woman on the cover of one of its catalogs in 2014 with her arms around two young children, and the caption, “Being their aunt means when we’re #together, there are no rules,” Melanie Notkin said her social media feed lit up.

“It was like, ‘Look at this, they recognize us,’” Ms. Notkin said.

After all, this is a population that spends money. A report by Ms. Notkin and DeVries Global, a public relations and marketing company, noted that women without children spend on average twice as much on beauty- and hair-related products a month than their counterparts with children do; they also spend 60 percent more days abroad.

Perhaps more surprisingly, women who don’t have children also spend 35 percent more on groceries per person a month than mothers do. It’s not clear why, but Heidi Hovland, chief executive of DeVries, said it might be because childless women and couples are buying more premium food items than families are, because groceries aren’t “about what the kids will and won’t eat.”

There have been some successful campaigns aimed at this group. In 2014, the Westin New York Grand Central hotel ran a promotion called “Womanhood Redefined,” aimed at women without children and including a consultation about healthful eating with the hotel’s executive chef and its running expert.

Melissa Braverman, then the hotel’s marketing manager, said in an interview in The New York Times that the package reflected her own life as a 40-year-old single woman without children.

“I think those of us who aren’t following the quote-unquote traditional trajectory are made to feel ‘other’ despite the fact that we represent half of the women of childbearing age in this country.”

Not surprisingly, it may be women like Ms. Braverman who will start pushing from the inside to include childless women.

“More enlightened clients are waking up to the not-mum,” said Rachel Pashley, group planning head with J. Walter Thompson in London, who wrote about this phenomenon in the British newspaper The Independent. “And even if you are a mum, you don’t want to be portrayed solely as a mum.”

Ms. Bailey agreed, saying that “very smart marketers are waking up” to the idea that women don’t want to be portrayed just as mothers — or spouses.

“How about a car commercial where the woman is not the passenger of some hot dude, or picking up her kids, but just living her life?” she said.

Companies are discovering that it can pay to dip into the child-free pond. The Westin package generated “tremendous social media exposure and buzz for the Westin Grand Central,” along with 420 inquiries about the package, said Bob Jacobs, vice president for brand management at Westin Hotels & Resorts North America. It has offered similar packages at some of its other hotels.

The TD Bank Group came across Ms. Notkin’s PANKs research and decided to see how it applied to Canadian women by commissioning a study of 6,149 women without children.

It found that nearly six in 10 Canadian women without children said they had a close relationship with a niece or nephew, or child of a friend. And while they shower these children with gifts and outings, they don’t necessarily set up trusts or savings accounts for them.

TD Bank used this information to target national and regional media and to educate its own advisers on “how to help them think in a different way when talking to professional women” said Sandy Cimoroni, senior vice president for shared services and chief operating officer of TD Wealth. That means urging them to set a little — or a lot — aside for that special child in their life.

Ms. Wright said it was difficult to get sponsors for her NotMom conference, partly because it was new, and small, attracting just over 100 people (although from five countries), but also because her participants didn’t seem to fit easily into a category. She hopes she might have better luck at the second conference, to be held in October 2017, also in Cleveland.

“This is going to be the challenge for advertisers,” Ms. Wright said. Women without children “have money and are beginning to get a little ticked off no one is noticing them. Advertisers haven’t figured out how to pay attention to us, but if the numbers continue to grow globally, they’ll have to.”

A version of this article appears in print on , on Page BU3 of the New York edition with the headline: Childless Women to Marketers: We Buy Things Too. Order Reprints | Today’s Paper | Subscribe